In the past, electronic products requiring high power such as automobiles, mobile phones, and notebook computers generally use nickel-cadmium batteries or lead-acid batteries. However, lead and cadmium metals generated by such batteries easily pollute the environment; therefore, nowadays most electronic products use lithium-ion batteries instead. Lithium batteries can be classified into primary batteries that use lithium metal or a lithium alloy as the negative electrode material and use a non-aqueous electrolyte solution and rechargeable batteries that generate electricity by means of movement of lithium ions between the positive electrode and the negative electrode. The batteries commonly used in the 3C industry and the automobile industry are lithium ion batteries, briefly referred to as lithium batteries.
FIG. 1 and FIG. 2 are a schematic view and a sectional view of a package structure of a soft package lithium battery in the prior art. A lithium battery in the prior art mainly includes a soft case 10. In existing products, the soft case 10 is mostly formed by correspondingly joining two aluminum composite films 11 and 12. Commonly used aluminum composite films 11 and 12 each have an adhesive layer on its inner side, and the adhesive layer becomes sticky after being melted by heat; therefore, the peripheries of the two aluminum composite films 11 and 12 can be laminated by means of a hot press lamination process.
An electrode plate set 20 and tabs 21 and 22 for electrical conduction of the positive electrode and the negative electrode are wrapped in the soft case 10, and the tabs 21 and 22 are partially exposed out of the soft case 10. In practice, the electrode plate set 20 consists of a plurality of positive electrode plates and a plurality of negative electrode plates. Then the tabs 21 and 22 are respectively electrically connected to positive and negative lugs of the electrode plate set 20. Finally, the peripheries of the two aluminum composite films 11 and 12 are directly press-fit by means of hot press lamination. A bonding adhesive may be additionally provided on sealing portions 13 on an upper surface and a lower surface of the tabs 21 and 22 for electrical conduction of the positive electrode and the negative electrode, so that an airtight effect is achieved when the aluminum composite films 11 and 12 are press-fit to the tabs 21 and 22; alternatively, the aluminum composite films 11 and 12 are respectively adhered to the sealing portions 13 on the upper and lower surfaces of the tabs 21 and 22 directly by means of hot press lamination.
However, in the charging/discharging process, gases generated inside the lithium battery due to overheat cause the soft case 10 to expand, and the gases form an outward stress 30. At the sealing portions 13 of the aluminum composite films 11 and 12 that are connected to the tabs 21 and 22, the stress 30 continuously impacts on the sealing portions 13, and because in this case the outward expanding direction of the aluminum composite films 11 and 12 is the same as the stripping direction, the stress 30 has a direct impact on the bonding effect of the aluminum composite films 11 and 12 at the sealing portions 13. In addition, the adhesive becomes soft due to the hot gases and starts to flow with reduced stickiness, which, together with the impact of the stress 30, leads to that pores are easily formed on the sealing portions 13 of the aluminum composite film 11 that cover the tabs 21 and 22. As a result, the electrolyte inside the soft case 10 flows out from the pores, causing damage to the battery and greatly reducing the service life of the battery.